Fix: ensure interface and prototype nodes are culled.

this commit ensures that schema interface node prototypes
are removed from the tree
They are not removed by schema_solve, and that is OK because
I think they need to be reused anyway.

they should be removed before attempting execution because they do nothing (but maybe cause bugs)

readtree.py

@@ -409,8 +409,8 @@ def parse_tree(base_tree, error_popups=False):
         nc = all_mantis_nodes.pop()
         if nc in array_nodes:
             continue
-        if nc.node_type in ["DUMMY"]:
-            continue
+        if nc.node_type in ["DUMMY", 'SCHEMA', 'DUMMY_SCHEMA']:
+            continue # screen out the prototype schema nodes, group in/out, and group placeholders
         # cleanup autogen nodes
         if nc.signature[0] == "MANTIS_AUTOGENERATED" and len(nc.inputs) == 0 and len(nc.outputs) == 1:
             from .base_definitions import can_remove_socket_for_autogen